1. Field of the Invention
This invention relates to electro-rheological hydraulic control valves, and more particularly to an improved valve that has a reduce power consumption, enhance performance, and provides fail-safe shut-off in normal mode and failure mode operation.
2. Description of the Prior Art
As will be appreciated by those skilled in the art, electro-rheological fluids are slurries typically comprised of a non-conducting fluid and particulates. A typical slurry contains about 30% particulates and about 6% water by weight, mixed in a dielectric liquid. The application of a high-voltage electric field across a small gap filled with a electro-rheological fluid causes the water absorbed in the particulate to form induced dipoles which align the particles between the electrodes, resulting in an effective change in viscosity in the localized area between the electrodes. The particulates are normally on the order of 10 to 50 microns in diameter, and may be either hard or soft. Electro-rheological materials and some applications are discussed in more detail in the literature, including the following articles, which are incorporated herein by reference.
Cyanamid, "Electro-Rheological Fluids", American Cyanamid Company, Wayne, N.J.
Machine Design, "Fluids That Thicken Electrically", by Theodore G. Duclos, Debra N. Acker and J. David Carlson, Thomas Lord Research Center, Lord Corporation, Cary, N.C.; Jan. 21, 1988.
Phys. Technology, Vol. 14, 1983, The Institute of Physics, "Electrorheological Fluids" by J. E. Stangroom.
One of the advantages of using electro-rheological (E-R) fluids is that their use allows direct flow control of the fluid by an electrical circuit. This eliminates the need for intermediate control steps that normally increase the response time of a system.
In prior art E-R valves, the complete shut-off of fluid flow is accomplished by increasing the voltage gradient across the fluid to a value where the shearing resistance of the fluid precludes fluid flow. However, this prior art shut-off method requires the application of continuous power to the valve in a shut-off mode. This is disadvantageous in terms of energy efficiency, and may damage the E-R fluid in the valve due to resistance heating. Further, in the event of an electrical failure, such valves lack a fail-safe operation for shut off.